The present invention relates to a method for producing a linear spring by simultaneously advancing desired two or more forming tools perpendicular or substantially perpendicular to a centerline of a quill in an extension direction of the centerline of the quill and colliding them against a linear material fed from a tip end portion of the quill under the condition that three or more forming tools arranged radially about the centerline of the guide for guiding the linear material are swivelled through a desired angle about the centerline of the quill, and relates also to an apparatus that is suitable for embodying this method.
Linear springs are categorized into a variety of coil springs such as a compressive coil spring, a tension coil spring, a twist coil spring or the like, and a linear worked spring that has no coil portion. Except for the compressive coil spring, in general, these linear coil springs are formed into a complicated shape having hooks in various directions and portions bent at various angle. Recently, the variety of coil springs have to be produced in a single linear spring forming apparatus.
Examples of the conventional linear spring forming apparatus that meets such a requirement are shown in Japanese Patent Application Laid-Open No. 144542/1984 entitled "METHOD FOR CONTROLLING FORMING TOOLS IN A LINEAR MATERIAL BENDING AND FORMING MACHINE", Japanese Patent Publication No. 2296/1994 entitled "SPRING FORMING METHOD AND APPARATUS", or the like.
The apparatus disclosed in the above-described Japanese Patent Application Laid-Open No. 144542/1984 relates to a system in which two or more forming tools which are arranged at predetermined radial position about the center of a quill are advanced perpendicular or substantially perpendicular right angle relative to a centerline of the quill in an extension direction of the centerline of the quill and collided against a linear material fed from a tip end portion of the quill, by the rotation of a cam driven by a plurality of motors whose rotational speed may be controlled. Each forming tool is fixed in an arrangement position relative to the quill. As a result, in some cases, it is impossible to advance the optimum forming tool in the extension direction of the centerline of the quill from the optimum direction even if the linear material is bent in a desired direction. Accordingly, in order to bend the material, it is necessary to prepare forming tools having a variety of special shapes for advancing the forming tools in the extension direction of the centerline of the quill from a different direction which is not on the extension line of the optimum direction for bending the linear material. Also, even if the forming tools in such a variety of special shapes would be prepared, in some cases, it is impossible to bend the linear material in a desired direction. The conventional method suffers from such a problem.
On the other hand, the apparatus disclosed in the above-described Japanese Patent Publication No. 2296/1994 relates to a system in which a single forming tool disposed in confronting relation with the extension line side of the centerline of the quill is swivelled about the centerline of the quill, and is brought into abutment with the linear material fed from the tip end portion of the quill to form the linear spring. Since all the forming are carried out by the single forming tool, there is no problem in forming of a larger coil portion having a long radius of curvature. However, in case of the bending forming step in which the radius of the curvature of the hook portion is short, as shown in FIG. 19, an edge at the linear material outlet of the tip end portion of the quill has to be utilized. Accordingly, in order not to produce a fault in the linear material, the line material has to be fed finely in conformity with a timing or time when the tool is advanced in the direction toward the tip end of the quill and is brought into contact with the linear material and to have a bent angle by increasing and decreasing a feed amount. Accordingly, it is necessary to keep the radius of curvature for the bending two to three times or more of the diameter of the linear material. In addition, such a bending forming method has to be carried out. In many cases, not only a precision of the bent angle is inferior but also the production speed has to be set at a low level. Moreover, in the case where the linear material is bent and formed with a short radius of curvature along the edge of the quill in forming, an increased pressure is applied to the linear material. Accordingly, it is impossible to avoid the fault in the linear material caused by a friction due to the contact between the quill and the edge. As a result, the conventional system always suffers from a serious problem in quality, and at the same time, a fatal default that it is impossible to form a bend having a very short radius of curvature in view of the quality requirement.
Also, in the apparatus disclosed in the above-described Japanese Patent Publication No. 2296/1994, unless there is formed a substantially semicircular shape which has no portion corresponding to half an upper portion in the tip end of the quill as shown in FIG. 20 for the forming of the coil portion, it is impossible to form the coil portion which is similar to a high density winding. The peripheral portion at the outlet of the linear material has to take a structure that is very thin in thickness. Accordingly, except for the case of an extremely thin linear material, not only it is necessary to avoid a fear of a damage of the quill in forming in this direction, but also in some cases, since the cutting tool for the linear material is fixed in position, it is impossible to cut the linear material after the forming operation depending upon a shape of the products which have been produced. Accordingly, for these reason, in some cases, the forming has to be given up. Thus, there are many disadvantages in the conventional system.
There is the following fatal defect in the case where such a structure for swivelling the forming tool about the centerline of the quill whenever the linear material is bent. As described above, since the forming tool is disposed on the extension line side of the centerline of the quill, it is impossible to set a plurality of forming tools. Accordingly, when the linear material is bent in a desired direction, it is impossible to use a plurality of forming tool-suitable for such bends. Thus, it is impossible to perform the forming of the variety of linear springs due to the limit to be caused to shapes otherwise feasible.
Also, an apparatus has been recently on the market in which the arrangement position of the forming tools arranged radially about the quill may be adjusted in position by a manual work. However, in such an apparatus, an interval (i.e., an angle) between the adjacent forming tools is limited to about 15.degree. due to factors in structure of the slide guide for supporting and operating the forming tools. In addition, once the arrangement position of the forming tools is moved and adjusted by the manual work, the apparatus is used in a fixed position of the forming tools at the set position. Accordingly, there is no difference from the position of the forming tools in the case where a single kind of the products are produced. There is no improvement in the fault that it is impossible to advance the optimum forming tool at a right angle or substantially a right angle relative to the centerline of the quill in the extension line direction of the centerline of the quill always from an optimum direction in forming the linear springs. Then, in the case where the displacement between the direction (angle) in forming the linear material and the direction in which the forming tool may be advanced is large, it is impossible to perform the forming operation. In case of the small displacement, the tool to be collided against the linear material and the special unit having a power source such as an air cylinder or the like is forcibly pushed against the forming portion just before the forming or the forming portion during the forming operation, whereby a desired forming direction (angle) is kept by twisting the linear material. This is a currently performed method. However, since the forming operation is carried out while twisting the linear material in this way, the maintenance of the forming precision is very unstable, and it takes a long time for the preparation work. In addition, although it is possible to form the linear springs having a shape to some extent, the production speed has to be reduced in view of the alignment of timing with the twist of the linear material by utilizing the air cylinder as a power source as described above and further the maintenance of the sufficient forming precision, such being the current situation.
Furthermore, in producing the linear springs, not only a mass production but also a production of a prototype or a very small amount of the production is required for various linear springs. In the case where such a small amount of the production for various linear springs is carried out, since exactly the same arrangement and kind of the forming tools and the auxiliary means for the mass production are required, the number of the kinds of the forming tools is very much increased.
However, if it is possible to the optimum forming tool from the optimum direction in the direction perpendicular or substantially perpendicular to the centerline of the quill in the extension direction of the quill, it is possible not only to reduce the number of the forming tools and to readily perform the preparation, but also to solve problems of the increase in the cost entailing from preparation of a variety of forming tools and the management thereof. However, in any type of the conventional linear spring forming apparatus, when the linear springs having various shapes are formed, there is the defect that it is impossible to advance the optimum forming tool from the optimum direction in the direction perpendicular or substantially perpendicular to the centerline of the quill in the extension line direction of the centerline of the quill. Accordingly, it is impossible to solve the cost problem and troublesome management problem.